Elucidating the Molecular -Scale Mechanisms of Zinc Adsorption on Redox -Active Ligand Tethered to Mesoporous Silica

This work develops innovative functional sorbents for the selective capture of zinc where these functional sorbents are tuned by tethering redox-active ligands such as Nile Blue A (NB) on mesoporous silica using 2-(3-aminopropylamino) silane (Si-A2) as the linker.This ligand was chosen due to its activity in selectively capturing Zn(II) via conventional routes.Selective Zn(II) capture efficiencies of 80% or higher are achieved.This functionalized sorbent achieved more than 80 % zinc capture via the conventional adsorption method.Recently, theoretical quantum calculation has claimed huge importance in analyzing molecular structure, stability, and functionalized surface properties.Additionally, quantum chemical analysis has proved significant in evaluating in-depth information regarding molecular energy, charge distribution, and chemical bonds for a wide range of molecular sizes.In this research, we have used DFT calculations using B3LYP/6-31G(d) to explore the molecular adsorption mechanism, such as adsorption energies, active adsorption sites, optimized geometries, charge distribution, molecular orbital analysis, and global reactivity indexes.The adsorption mechanism of Zn(II) on an unfunctionalized silica substrate, N-(2-Aminoethyl)-3-aminopropyltriethoxysilane (used as linker), Nile blue A (used as a ligand) and linker-ligand tethered silica were investigated.The DFT simulations have further enlightened that the formulated adsorbent molecule can adsorb a maximum of three Zn(II) ions, while the unfunctionalized silica substrate can adsorb only one Zn(II) ion.The adsorption energy values ensure the chemisorption process and the in-depth analysis of global reactivity indexes and charge transfer confirms the formation of covalent coordination bonds and electrostatic interactions during adsorption.This research work validates the experimental observations through theoretical calculations and proves the excellent applicability of DFT techniques to design efficient functional materials with fewer experimental trials.